This application claims priority to Korean Patent Application No. 10-2004-0051974, filed on Jul. 5, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an analog semiconductor device and a method of manufacturing the same, and more particularly, to an analog semiconductor device having a multi-layer dielectric film and a method of manufacturing the same.
2. Description of the Related Art
Analog capacitors are used in analog-to-digital converters (AD converters), RF devices, switching capacitor filters, CMOS image sensors (CISs), and the like. When a voltage applied to an analog capacitor is changed, the electric charge applied to electrodes surrounding a dielectric film is also changed. Analog capacitors retain signal information that is based on the variation of the electric charge.
In general, when a voltage (V) is applied to a capacitor, the electric charge of the electrodes can be expressed by the following equation:Q=C×V,where C denotes an electrostatic capacitance, that is, a capacitance, and V is the voltage.
When the capacitance (C) is constant, the electric charge (Q) is linearly proportional to the voltage (V). When the voltage (V) is constant, the electric charge (Q) of the capacitor is linearly proportional to the capacitance (C). Assuming such a linear relationship, the operating voltage range of the capacitor can be quantized into a plurality of steps and each of the quantized voltages can correspond to a bit of a binary number.
In order to obtain a large number of bits from an analog capacitor, the difference in electric charge corresponding to each of the quantized voltages must be large and constant. Therefore, analog capacitors are composed of a dielectric film having the property of an excellent voltage coefficient of capacitance (VCC). A dielectric film with excellent VCC ensures that, when a voltage is applied to the capacitor, the capacitance is almost constant and is sufficiently large, and that leakage current is small.
High integration of analog semiconductor devices results in the requirement for smaller capacitors. With the smaller size, in order to prevent a decrease of capacitance, a high-k dielectric film is used. In this case, the high-k dielectric film is defined as a dielectric film having a dielectric constant of 8 or greater.
Meanwhile, the capacitance of a capacitor generally depends on applied voltage. That is, the capacitance C(V) is a function of an applied voltage (V). The capacitance C(V) can be expressed as:C(V)=C(0)×(a×V2+b×(V+1)),where C(0) denotes the capacitance of the capacitor at an applied voltage of 0 V, a denotes a quadratic voltage coefficient of capacitance (VCC), and b denotes a linear VCC. Accordingly, in order to have a small VCC, a and b each should be 0 or nearly 0, and in particular, a should be nearly 0.
The quadratic coefficient a depends on interfacial characteristics between the electrodes and the dielectric film of a capacitor. That is, when a voltage is applied, when depletion occurs in the electrodes, the quadratic coefficient a becomes negative. On the other hand, when electrons flow to the dielectric film, thereby decreasing the effective thickness of the dielectric film, the quadratic coefficient a becomes positive.
The dielectric film of an analog capacitor is preferably a high-k dielectric film having a small leakage current and a quadratic VCC a having a small absolute value. However, currently, leakage current characteristics and voltage efficiency characteristics for analog capacitor cannot be satisfied by the use of a single high-k dielectric film.
In order to overcome this problem, multi-layer dielectric films have been employed in the manufacture of analog capacitors. An example of such a capacitor is disclosed in “Capacitor with Multi-component Dielectric and Method of Fabricating the Same” (U.S. Pat. No. 6,341,056), by Allman et. al.
However, in such capacitors, reaction between the multi-component dielectric film with the electrodes needs to be reduced. In addition, an improvement in leakage current characteristics at high temperatures, shortening of the manufacturing process of the multi-layer dielectric film, and prevention of contamination in the multi-layer dielectric film are needed.